Currently, the SEM is widely used for observation of a sample having a size ranging from submicron order to nanometer order. The SEM forms an image by irradiating a sample with primary electrons emitted from an electron source while scanning the primary electrons, and detecting secondary electrons caused in the sample. Note that the secondary electrons are divided into “true” secondary electrons characterized in that they have energy equal to or lower than 50 eV and backscattered electrons having energy about the same as incident energy of the primary electrons. A contrast image reflecting the shape of pattern surface, the potential, the difference in work function and the like is obtained from the “true” secondary electrons. On the other hand, a contrast image reflecting the difference in composition and crystal orientation of the sample is obtained from the backscattered electrons.
In recent years, SEMs commercialized as products by respective companies are equipped with plural detectors to obtain various contrast images. On the other hand, image contrast interpretation has become difficult, and there is an increasing need for quantitative analyses of secondary electron energy detected under respective conditions. In addition, to reduce sample damage accompanying observation of sample top surface and irradiation of primary electrons and image disorder due to electrical charge, it is required to perform energy analyses of secondary electrons under the condition that irradiation energy of the primary electrons is low. The techniques of secondary electron energy spectroscopy are disclosed in, e.g., Patent Literatures 1 and 2.